A wearer may be prescribed a positive, null or negative optical power correction. For presbyopic wearers, the value of the power correction is different for far-vision and near-vision, due to the difficulties of accommodation in near-vision. Ophthalmic lenses suitable for presbyopic wearers are multifocal lenses, the most suitable being progressive multifocal lenses.
This present invention relates to mid-distance ophthalmic lenses that is to say lenses that do not have any far vision zone. Such lenses are not “progressive addition lenses” in the classical sense of the term. They are neither single vision lenses since they have at least one near vision zone and an intermediate vision zone, nor bifocal or trifocal lenses since they have at least one progression zone between their near vision zone and the intermediate vision zone.
Literature data on the use of computer screens show a great variability at the viewing distance, see for instance Jaschinski 2002 “The proximity-Fixation-Disparity curve and the preferred viewing distance at a visual display as an indicator of near vision fatigue”, Optometry and Vision Science; Vol. 79, No. 3, pp 158-169. In this paper, authors measured the distance to the screen for 40 individuals free to place their screen as comfortable as possible. Results showed a distance between the eye and the computer screen equal to 63±25.5 cm.
The average size of recent TV screens is 36/37 inches, which corresponds to a viewing distance of 190±50 cm. However, the TV screen size are ranging from 20 to 80 inches which results in distance to the screen highly variable. The television screen may also be placed on the floor or on furniture which results in lowering of gaze direction also highly variable.
Likewise, the viewing distance of a computer screen, or of a tablet, or of an eBook reader, or of a smartphone varies with the average size of the screen.
For example, the average size of a computer screen is about 15 inches, with a ratio between the height and the width of 1.7, which corresponds to a mean viewing distance of about 63 cm, with a standard deviation of 13 cm.
As another example, for a tablet with an average size superior to 8.5 inches, with a ratio height/width of the tablet between 0.62 and 0.75, the mean viewing distance is of about 39.7 cm with a standard deviation of 6 cm.
For example, the average size of a eBook reader is 6 inches, with a ratio between the height and the width of 0.75, which corresponds to a viewing distance of about 38 cm with a standard deviation of 6.5 cm, and the average size of recent smartphones is 5 inches, with a ratio between the height and the width of 0.56, which corresponds to a mean viewing distance of about 33.8 cm with a standard deviation of 5.1 cm.
If one considers a mid-distance lens, or “occupational lens” or “degressive-power lens” as defined in § 8.3.6 in ISO 13666:2012, whose near vision zone, intermediate vision zone are calculated from an average posture, one can easily understand that a single lens will not suit everyone because of the variety of screen types, and the wearer individual variability in screen uses.
Therefore, there is a need for an ophthalmic lens that is adapted to the individual variability in screen uses, mainly for new electronic screens.
One object of the present invention is to provide such ophthalmic lenses for improving the comfort of a wearer reading a text or working with new electronic screens.